Port 445: SMB

What is port 445 used for?

Windows file and printer sharing (Server Message Block).

Should port 445 be open?

Don’t expose to the internet. Keep this port on private networks and reach it through a VPN or SSH tunnel. SMB exposed to the internet was the entry point for WannaCry. Use a VPN for remote file access.

See what is listening on port 445

# Linux
sudo ss -tlnp | grep ':445 '

# macOS
sudo lsof -nP -i TCP:445 -sTCP:LISTEN

# Windows (PowerShell)
Get-NetTCPConnection -LocalPort 445 -State Listen

Open or block port 445 in a firewall

# Ubuntu / Debian (ufw)
sudo ufw allow 445/tcp
sudo ufw deny 445/tcp

# Windows (PowerShell, as administrator)
New-NetFirewallRule -DisplayName "Port 445" -Direction Inbound -Protocol TCP -LocalPort 445 -Action Allow

On cloud servers, also open the port in the provider’s security group or network firewall. At home, a service behind a router needs a port-forwarding rule to the device’s local IP.

Test it from outside

A port can be open on the server but blocked upstream. The Port Checker connects from the internet, so it shows what the world sees. From your own machine, use nc -vz example.com 445 (macOS/Linux) or Test-NetConnection example.com -Port 445 (Windows).